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• Reusing Decoder instance for multiple png files [ffmpeg]

  21 mars 2016, par gaurav

  In my code i am decoding multiple png files. for each file i create a AVCodecContext instance , open the codec , decode the file and finally close the codec. I tried reusing the same AVCodecContext instance for all the png files but it doesn’t work. i get bugged out (random colours) images when I display them on screen. Below is my code which works but it creates AVCodecContext object every time given function is called.

  int ImageSequence::decodeFromByteArray(uint8_t *inbuf , AVFrame **frame , int dataLength){
  
      AVCodec *codec = avcodec_find_decoder(AV_CODEC_ID_PNG);
  
  
  
      AVCodecContext *codecCtx = avcodec_alloc_context3(codec);
  
  
  
      if(!codecCtx){
  
          av_log( NULL , AV_LOG_ERROR , "Cannot allocate codec ctx \n");
  
          return -1;
  
      }
  
  
  
      if(codec->capabilities&CODEC_CAP_TRUNCATED)
  
      {
  
          codecCtx->flags|= CODEC_FLAG_TRUNCATED; /* we do not send complete frames */
  
      }
  
  
  
  
  
      if (avcodec_open2(codecCtx, codec, NULL) < 0){
  
          av_log( NULL , AV_LOG_ERROR , "cannot open decoder \n");
  
          return -1;
  
      }
  
  
  
      AVPacket pkt;
  
      int ret;
  
  
  
      av_init_packet(&pkt);
  
  
  
      pkt.size = dataLength;
  
      pkt.data = inbuf;
  
  
  
      int got_frame , len;
  
  
  
      len = avcodec_decode_video2(codecCtx, *frame, &got_frame, &pkt);
  
  
  
      if(got_frame){
  
          ret = 1;
  
      }else{
  
          ret = -1;
  
      }
  
  
  
      av_free_packet(&pkt);
  
      //free decoder resources
  
      avcodec_free_context(&codecCtx);
  
      avcodec_close(codecCtx);
  
  
  
      return ret;
  
  }

  Couple of questions -
  1) Is it possible to use same AVCodecContext object for multiple image files.
  2)If yes then what i should do to reset the state of decoder after decoding each image file.

• FFMPEG Blending for VP9 format videos

  28 novembre 2022, par OneWorld

  I get a darker background, almost like a placeholder for the asset that is to be blended, whereas the background should be transparent, and should show the same colour as the rest of the background.

  


  I have two webm vp9 files that I am trying to blend using FFMPEG blending functionality.

  


  One of the videos is a zoom animation that starts from 1 pixel in size and then increases in size to 50 x 50 pixels.

  


  The other is a solid red background video 640 px x 360 px

  


  At frame 1 the result looks like this :-


  


  At about 0.5 seconds through, the result looks like this :-


  


  At the end of the sequence, the zoom animation webm fills that darker square you see (50 x 50 pixels).

  


  The code to do the blending of the two webm files looks like this :-

  


  filter_complex.extend([
        "[0:v][1:v]overlay=0:0:enable='between(t,0,2)'[out1];",
        '[out1]split[out1_1][out1_2];',
        '[out1_1]crop=50:50:231:251:exact=1,setsar=1[cropped1];',
        '[cropped1][2:v]blend=overlay[blended1];',
        "[out1_2][blended1]overlay=231:251:enable='between(t,0,2)'[out2]"
    ])


  


  This overlays a red background onto a white background, making the red background the new background colour.
It then splits the red background into two, so that there is one output for cropping and another output for overlaying.
It then crops the location and size of the layer to be blended out of the red background. We do this because blending works only on an asset of the same size.
It then performs the blend of the zoom animation onto the cropped background.
It then overlays the blended over the red background

  


  Unfortunately I'm unable to attach videos in stackoverflow, otherwise I would have included them.

  


  The full command looks like this :-

  


  ffmpeg -i v1_background.webm -itsoffset 0 -c:v libvpx-vp9 -i v2_red.webm -itsoffset 0 -c:v libvpx-vp9 -i v3_zoom.webm -filter_complex  "[0:v][1:v]overlay=0:0[out1];[out1]split[out1_1][out1_2];[out1_1]crop=50:50:231:251:exact=1,setsar=1[cropped1];[cropped1][2:v]blend=overlay[blended1];[out1_2][blended1]overlay=231:251"  output_video_with_blended_overlaid_asset.mp4


  


  I have checked the input vp9 webm zoom video file by extracting the first frame of the video

  


  ffmpeg -vcodec libvpx-vp9 -i zoom.webm first_frame.png


  


  and inspecting the colours in all the channels in GIMP. The colours (apart from the opaque pixel in the middle) are all zero, including the alpha channel.

  


  Note that I tried adding in all_mode, so that the blend command is blend=all_mode=overlay, however this still shows the darker placeholder under the animation asset. In other words, this command

  


  ffmpeg -i v1_background.webm -itsoffset 0 -c:v libvpx-vp9 -i v2_red.webm -itsoffset 0 -c:v libvpx-vp9 -i v3_zoom.webm -filter_complex  "[0:v][1:v]overlay=0:0[out1];[out1]split[out1_1][out1_2];[out1_1]crop=50:50:231:251:exact=1,setsar=1[cropped1];[cropped1][2:v]blend=all_mode=overlay[blended1];[out1_2][blended1]overlay=231:251"  output_video_with_blended_all_mode_overlay_asset.mp4


  


  also doesn't work

  


  and trying to convert the formats to rgba first doesn't help either, command below is simplified a bit

  


  ffmpeg -c:v libvpx-vp9 -i v2_red.webm -c:v libvpx-vp9 -i v3_zoom.webm -filter_complex "[0:v]format=pix_fmts=rgba[out1];[1:v]format=pix_fmts=rgba[out2];[out1]split[out1_1][out1_2];[out1_1]crop=50:50:0:0:exact=1,setsar=1[cropped1];[cropped1][out2]blend=all_mode=dodge[blended1];[out1_2][blended1]overlay=50:50" output_video_with_blended_all_mode_dodge_rgba_and_alpha_premultiplied_overlay.mp4


  


  adding in an alpha premultiply didn't help either

  


  ffmpeg -c:v libvpx-vp9 -i v2_red.webm -c:v libvpx-vp9 -i v3_zoom.webm -filter_complex "[0:v]format=pix_fmts=rgba[out1];[1:v]setsar=1,format=pix_fmts=rgba,geq=r='r(X,Y)*alpha(X,Y)/255':g='g(X,Y)*alpha(X,Y)/255':b='b(X,Y)*alpha(X,Y)/255'[out2];[out1]split[out1_1][out1_2];[out1_1]crop=50:50:0:0:exact=1,setsar=1[cropped1];[cropped1][out2]blend=all_mode=dodge[blended1];[out1_2][blended1]overlay=50:50" output_video_with_blended_all_mode_dodge_rgba_and_alpha_premultiplied_overlay.mp4


  


  Wondering if there is a workaround I could use so that the background stays transparent ?
I was looking for maybe a way of changing the input pixel format in the filter_complex stream to see if that works, but couldn't see anything about this.

  


• Hareware accelerated HEVC encode/decode in python on Intel x64 with Nvidia GPU [closed]

  24 mars 2021, par Jason M

  I am working on a python project of decoding a 4k@25fps hevc stream from a IP camera, processing it, croping some region-of-interest and encoding each into a new stream. The program runs on a Intel i7-10700 PC with NVidia Gtx1080. I see that opencv offers Intel MediaSDK support and cuda codec, while Nvidia offers PyNvCodec.

  


  What may be my best combination of hardware-accelerated encoding/decoding options ? A demo project would be nicer.